Hand microphone for sound recording and reproducing instruments with ac switching

ABSTRACT

A hand microphone for use with sound recording and reproducing instruments and including a control portion from which various control functions can be initiated in the instrument, one of which control functions involves switching an alternating voltage circuit, the unit for switching such circuit including a transistor having its collector-emitter path connected in series in such alternating voltage circuit and a mechanically stationary electronic switch connected to the base of the transistor for applying thereto, when the electronic switch is closed, a bias voltage which causes the transistor collector-emitter path to conduct current in both directions.

United States Patent [151 3,636,271 Rodenbeck 1 Jan. 18, 1972 54] HANDMICROPHONE FOR SOUND FOREIGN PATENTS OR APPLICATIONS RECORDING ANDREPRODUCING INSTRUMENTS WITH AC SWITCHING Jorg Rodenbeck, Wilhelmshaven,Germany Olympia Werke AG, Wilhelmshaven, Germany Filed: Dec. 9, 1969Appl. No.: 883,031

Inventor:

Assignee:

[30] Foreign Application Priority Data Dec. 18, 1968 Germany ..P 18 15324.7

[5 6] References Cited UNITED STATES PATENTS 3,555,202 l/l97l Warnke..i79/lO0.lDR

no R w 1,282,089 11/1968 Germany ..l79/l0O.lDR

. OTHER PUBLICATIONS Hurley, Junction Transistor Electronics, i958, 339-342, 346-347.

Primary Examiner-Stanley M. Urynowicz. Jr. Assistant Examiner-Raymond F.Cardillo. .I r. Atlomey-Spencer & Kaye ABSTRACT A hand microphone foruse with sound recording and reproducing instruments and including acontrol portion from which various control functions can be initiated inthe instrument, one of which control functions involves switching analternating voltage circuit, the unit for switching such circuitincluding a transistor having its collector-emitter path connected inseries in such alternating voltage circuit and a mechanically stationaryelectronic switch connected to the base of the transistor for applyingthereto, when the electronic switch is closed, a bias voltage whichcauses the transistor collector-emitter path to conduct current in bothdirections.

4 Claims, 5 Drawing Figures H A games g RECORDING AND REPRODUCTNGINSTRUMENT ELECTRO- ACOUSTIC TRANDUCER 91 AC VOLTAGE SOURCE ELECTRONICSWITCHES 6 0 1 MICROPHONE SOLENOID PATENTED JAM 81972 SHEET 2 BF 2 T0RESISTOR l7 INVENTOR Jb'rg Rodenbeck ATTORNEY',

HAND MICROPHONE FOR SOUND RECORDING AND REPRODUCING INSTRUMENTS WITH ACSWITCHING BACKGROUND OF THE INVENTION The present invention relates to ahand microphone for sound recording and reproducing instruments,particularly for dictating equipment, which microphone is of a typecontaining a control portion from which various control functions can beinitiated in the main instrument, e.g., the functions of recording,playback, rewind and stop.

It is already known in the art to produce these control functions by oneor a plurality of control buttons which act on mechanical, metalliccontacts to initiate switching signals. These metallic control contacts,however, have only a limited service life and, what is perhaps theirgreatest drawback, the actuation of these metallic control contactsthrough the mechanical buttons causes strong, interfering noises, duringrecording due to the fact that these control means are disposed,together with a microphone capsule, in a common hand microphone housing.

In order to eliminate these drawbacks of the mechanical controlcontracts and control buttons, it has already been proposed for examplein German Pat. No. DAS 1,282,089, to provide electronic switching meanswithout movable contacts, i.e., mechanically stationary electronicswitching means, to perform the control functions in place of themechanical control buttons. Such movable contact-free electronicswitching means may include, for example, capacitor plates disposed inthe microphone housing so as to be externally influenced by thecapacitance of the operators hand in order to perform the same switchingfunction through an electronic switch as was previously performed by ametallic contact.

It is also possible to connectthe external leads of electricallyconductive plates with another conductive coating on the outside of themicrophone via the ohmic resistance of the operators hand to control anelectronic switch. At the output of these contact-free electroniccontrol means there is thus present, in almost all cases, an electronicswitch which replaces the original movable metallic control contact. Theelectrical properties of such control components in hand microphones arepreferably so designed that this microphone can easily be exchanged foranother microphone having movable metallic control contacts.

The necessity often arises, however, of using the movable mechanicalcontrol contacts in the hand microphone to directly switch alternatingvoltages, e.g., low-frequency voltages. The previously knowncontact-free electronic control means in hand microphones, however, weredesigned only for switching direct voltages and were not suited foralternating voltages. For this reason it was necessary to furtherconnect an electromagnetic relay or the like which was able to switchthe alternating voltage by means of its movable metallic contacts.

SUMMARY OF THE INVENTION It is an object of the invention to eliminatethe wear experienced by the control contacts in a hand-held microphone.

A further object of the invention is to reduce the cost of the controlunit provided in such a microphone.

It is a more specific object of the present invention to employ theprinciple of the fully electronic movable contact-free control of thefunctions in sound recording and reproducing instruments, particularlyin dictating equipment, for switching alternating voltages.

The present invention thus involves a hand microphone whose controlportion has movable contact-free electronic control means as asubstitute for the metallic control contacts and can directly switch, inat least one of its control positions, alternating voltages, e.g., thelow-frequency signals to be delivered to an electroacoustical transducerwhen the machine is in the playback condition. According to a basicfeature of the present invention, the collector-emitter path of atransistor is provided for selectively conducting the alternatingvoltages and the switching state of the transistor is controllable bythe associated movable contact-free electronic means to such an extentthat it is able to switch through the highest occurring alternatingvoltage peaks in the forward as well as in the reverse direction withoutbeing blocked.

The present invention thus makes it possible to connect thecollector-emitter path of a transistor to any desired movablecontact-free electronic control means in the hand microphone in order toswitch through alternating voltage signals in any desired operatingposition of the control portion. It is of course also possible to equipall the movable contact-free electronic control units of the controlportion in this manner in order to be able to switch alternatingvoltages as well as direct voltages.

The control of the transistor for switching through alternating voltagesignals is accomplished preferably in the manner that a switch-throughcontrol voltage can be applied to the base of the transistor by theelectronic means which is so high that sufi'rcient base current flows inthe forward direction during normal operation as well as during reverseoperation.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is the circuit diagram of aknown microphone with movable metallic control contacts.

FIG. 2 is the circuit diagram of a microphone according to the presentinvention connected to a main instrument for recording and reproducingsound.

FIG. 3 is the diagram of the microphone of the present invention.

FIGS. 4 and 5 shows the electronic switches 12 and 13.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the most importantelectrical components of a conventional hand microphone 10 for dictatingequipment. Terminals 1 through 7 are the connections through which thehand microphone is connected with the actual dictating equipment 20(FIG. 2). An operating voltage is applied through terminal 1 which isswitched, depending on the switching position of the slide switch, orbutton 8 to one of the four terminals 2 through 5. The switch 8 connectsthe operating voltage from terminal 1 with terminal 2 in position R(rewind), with terminal 3 in position W (playback), with tenninal 4 inposition H (stop) and with terminal 5 in position A (recording).Terminals 6 and 7 are connected with the electroacoustical transducer 9of the microphone.

FIG. 2 shows the hand microphone 10' according to the invention with anelectronic control portion which has no movable contacts and which is toperform the same functions as the control portion of the microphone ofFIG. 1. The switch 8 of FIG. 1 is here replaced by electronic means 12,l3, l4 and 15 which may be of any desired construction and which eachcontain an electronic switch which is here shown with the symbol of aswitch contact. As is well known, electronic switches do not rely fortheir operation on the physical movement between contact members andhence do not produce any contact noise, which would be picked up by themicrophone transducer. Terminal 1 is connected to a metallic coating 1 1near which there are disposed the metallic coatings 22, 23, 24 and 25which are associated with the four different switching positions R, W, Hand A. The finger of the operator can connect any coating 22, 23, 24 or25 with the main coating 11 so that an appropriate control signalreaches the associated contact-free control means 12, 13, 14 or 15.While the resistance provided by the operators finger is relativelyhigh, it is as is well known, sufficiently low to provide the currentnecessary to actuate many types of electronic switches, particularlythose of the semiconductor.

If for example, coating 22 is connected with coating II, the contactresistance conducts a control signal to the control means 12 (FIG. 4) toclose its electronic switch and thus apply the voltage at terminal 1 toterminal 2 and from there to the dictating equipment. This appliedvoltage actuates the appropriate function in the dictating equipment 20for rewinding. This applies similarly for the electronic control means14 and 15.

it can be seen that the circuits of conductors l, 2, 3, 4 and 5 of H6. 2can serve the same switching purposes as conductors l, 2, 3, 4 and 5 ofH6. 1. lf, for instance, electromagnetic solenoids are to be controlled,these have to be connected in series with a DC voltage, betweenconductor 1 and any of the conductors 2, 4 or 5.

If now the voltage at terminal 1 is connected through the metaliiccoating 23 to the input of the electronic control means 13 (FIG. 5), theassociated electronic switch is closed and a bias is applied, via theseries resistance 17 to the base of a transistor 16. This bias is, asshown, negative in the case of a PNP-transistor 16; for a NPN-transistorit would be positive. The collector-emitter path of the transistor 16thus becomes conductive and closes the loop containing an alternatingvoltage source 19 and an electroacoustical transducer 18, e.g., aspeaker, in the machine 20 through terminals 1 and 3.

During the positive half cycles of the alternating voltage from source19 (e.g., audiofrequency output), the terminal 3 which is connected tothe emitter of transistor 16 is positive with respect to line 1 so thatthe transistor operates normally in its conductive state. During thenegative half cycles of the alternating voltage from source 19, however,terminal 3 is negative and transistor 16 can only be kept in itsconductive stage if its base remains more negative than terminal 3. Forthis reason the negative bias voltage for the base must have a certainminimum value which is higher than the maximum occurring negativevoltage peaks of the alternating voltage from source 19. During thenegative half cycles of the alternating voltage from source 19 thetransistor 16 thus operates in the reverse direction. Account musttherefore be taken of the fact that an asymmetric transistor has a lowercurrent amplification in reverse conduction operation than in normalforward operation. One skilled in the art would be readily able toselect the appropriate transistor for a given circuit and to determinethe necessary bias voltage level which could be provided, for example,by a small battery in the microphone case.

In this way it is possible to switch through alternating voltage signalsof relatively high power to an electroacoustical transducer 18 withoutthe need for movable metallic contacts. If control signals of sufficientamplitude are applied to the base of transistor 16 distortions andlosses can be kept to a negligible maximum.

It is of course also possible to equip a plurality of these contact-freemeans 12 to with an additional transistor for switching throughalternating voltages. Under certain circumstances it might be advisableto provide appropriate additional transistors 16 for all channels. it isof course also possible to switch direct voltages by means of thecontrol structure connected to line 3.

FIG. 3 shows the hand microphone 10 with the metallic coating 11 at theback of the microphone housing and the associated coatings 22, 23, 25and 25, which represent the four different switching positions. Thefinger of the operator may connect the main coating 11 with any of thecoatings 22 to 25.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes andadaptations, and the same are intended to be comprehended within themeaning and range of equivalents of the appended claims.

I claim:

1. In a hand microphone for use with, and electrically connectable to, asound recording and reproducing instrument containing at least onealternating voltage circuit to be controlled from the microphone, theimprovement wherein said microphone contains circuit control meanscomprising: a transistor; connection means connected to the collectorand emitter of said transistor and connectable to the machine forconnecting the collector-emitter path of said transistor in series withsaid at least one alternating voltage circuit for permitting theconduction state of said transistor to control the operation of suchcircuit; mechanically stationary electronic switch means connected tosaid transistor, said switch means defining a conductive path which isselectively closeable for placing said transistor in a conductive statewith respect to all amplitude levels of the alternating voltage in suchcircuit; and operating means connected to said switch means forcontrolling the switching state thereof.

2. An arrangement as defined in claim 1 wherein said switch meanscomprises a bias voltage source and is connected to the base of saidtransistor for applying a base bias voltage which maintains a forwardbase current for either direction of current flow through thecollector-emitter path of said transistor.

3. An arrangement as defined in claim 2 further comprising additionalelectronic switch means connectable to control other circuits in theinstrument and each defining a conductive path which is selectivelycloseable, and additional operating means connected to said additionalswitch means for individually controlling the switching states thereof.

4. An arrangement as defined in claim 3 wherein said operating means andsaid additional operating means together comprise a common conductivestrip connectable to a voltage source and a plurality of individualconductive coatings spaced from said strip and each forming part of arespective operating means, and wherein said electronic switch means andadditional electronic switch means are of a type whose conductive pathis closed by the voltage applied thereto when said strip is connected tosuch voltage source and the gap between said strip and a respectivecoating is bridged by the finger of an individual using the instrument.

1. In a hand microphone for use with, and electrically connectable to, asound recording and reproducing instrument containing at least onealternating voltage circuit to be controlled from the microphone, theimprovement wherein said microphone contains circuit control meanscomprising: a transistor; connection means connected to the collectorand emitter of said transistor and connectable to the machine forconnecting the collector-emitter path of said transistor in series withsaid at least one alternating voltage circuit for permitting theconduction state of said transistor to control the operation of suchcircuit; mechanically stationary electronic switch means connected tosaid transistor, said switch means defining a conductive path which isselectively closeable for placing said transistor in a conductive statewith respect to all amplitude levels of the alternating voltage in suchcircuit; and operating means connected to said switch means forcontrolling the switching state thereof.
 2. An arrangement as defined inclaim 1 wherein said switch means comprises a bias voltage source and isconnected to the base of said transistor for applying a base biasvoltage which maintains a forward base current for either direction ofcurrent flow through the collector-emitter path of said transistor. 3.An arrangement as defined in claim 2 further comprising additionalelectronic switch means connectable to control other circuits in theinstrument and each defining a conductive path which is selectivelycloseable, and additional operating means connected to said additionalswitch means for individually controlling the switching states thereof.4. An arrangement as defined in claim 3 wherein said operating means andsaid additional operating means together comprise a common conductivestrip connectable to a voltage source and a plurality of individualconductive coatings spaced from said strip and each forming part of arespective operating means, and wherein said electronic switch means andadditional electronic switch means are of a type whose conductive pathis closed by the voltage applied thereto when said strip is connected tosuch voltage source and the gap between said strip and a respectivecoating is bridged by the finger of an individual using the instrument.